There is known a semiconductor device manufacturing process for forming a thin film having a multilayer structure on a wafer by sequentially performing various thin film processes (e.g., film formation, modification, heat treatment, etching and the like) on a semiconductor wafer (hereinafter, referred to as “wafer”).
Such semiconductor devices manufacturing process can be realized by a processing system having a cluster structure in which a plurality of processes can be consecutively performed by connecting a plurality of processing chambers to a single common transfer chamber. There is suggested a transfer method for sequentially transferring a wafer to processing chambers in the processing system configured as described above (see, e.g., Patent Document 1).
In order to consecutively and effectively perform desired processes in the processing chambers, it is preferable to effectively transfer the wafer. Therefore, in the above processing system, a transfer robot having two arms may be used to effectively transfer a plurality of wafers. Each of the two arms of the transfer robot is provided with a pick for holding a wafer. One pick holds and transfers an unprocessed wafer to a processing chamber. The other pick holds and transfers a processed wafer that has been subjected to a predetermined process in the transfer chamber to a next processing chamber. By holding a wafer on each of the two picks of the transfer robot, the wafer can be transferred more effectively compared to the case of using a transfer robot having one arm.
Patent Document 1: Japanese Patent Application Publication No. 2004-119635
However, a processed wafer unloaded from a heat treatment chamber for performing heat treatment on a wafer has a high temperature. Therefore, in order to hold the processed wafer unloaded from the heat treatment chamber, the two arms (including the picks) need to be made of a material that can withstand a high temperature.
Especially, when functions of the arms are fixed, the amount of heat applied to one arm is different from the amount of heat applied to the other arm. For example, when one arm has a function of transferring a wafer before processing (hereinafter, referred to as “unprocessed wafer”) and the other arm has a function of transferring a wafer after processing (hereinafter, referred to as “processed wafer”), a peak of a temperature of the arm for transferring the processed wafer is higher than that of a temperature of the arm for transferring the unprocessed wafer. As a result, it is difficult to distribute the amount of heat received during the wafer transfer to both arms, and the arm for transferring the processed wafer deteriorates faster than the arm for transferring the unprocessed wafer.